1. The field of art to which the invention pertains includes "Valves and Valve Actuation".
2. The prior art to which the invention is directed includes the art of butterfly valves being of a type in which a usually circular vane or disc is rotatable in a fluid body passage between an open and closed position. When in a closed position, the vane engages a seat with which it cooperates to provide a thruport seal against leakage of the pressurized line contents intended to be contained by the valve. It is desirable, if not essential, in valves of this type that the seal be effective on each occasion of valve closing for the life of the valve to continuously provide positive shutoff with minimum servicing of the components affording the seal.
For such purposes, one or other of the vane or seat is usually of a firm metal construction while the other supports an elastomeric gasket and which together cooperate during valve closure for effecting the desired thruport seal. Exemplifying butterfly valves of this type is the disclosure of U.S. Pat. No. 3,471,120 in which an adjustable vane supports the gasket for engagement against a stainless steel seat. As between the gasket and seat the former is usually the more flexible and relatively softer composition, rendering it highly susceptible to abrading and consequent wear in the course of valve operation. Where local enlargement of the gasket results in a scalloped periphery, the high spots may be excessive to obtain adequate sealing in the low spots causing excessive wear on the former. For obvious reasons such wear over a period of valve use frequently results in the need for maintenance, usually in the form of gasket readjustment or replacement. Either form of maintenance requires access to the valve internals and may even require removal of the valve from the pipeline for that purpose. Despite recognition of the problem, it has not been heretofore known how to retain the desirable flexible characteristics of the gasket while supporting it in a manner whereby the encountered abrading effect can be held to a minimum in order to decrease the high level of maintenance previously associated therewith.